1. Field of the Invention
The present invention relates generally modifying the local speed of sound characteristics of a gas or fluid flow, more particularly to modifying these characteristics using the distribution of a high molecular weight and/or low temperature gas into to the flow, and most particularly to attenuating the acoustic disturbance and/or noise associated with aircraft by modifying the local speed of sound characteristics using high molecular weight and/or low temperature gas upstream of the aircraft.
2. Description of the Related Art
Reduction of noise generated by jet engines has become an important aspect of aircraft design. Sound waves from aircraft traveling at subsonic speed propagate in all directions relative to the aircraft. The reduction of noise generated by aircraft has obvious benefits, including reducing noise pollution and, thereby, reducing safety risks to persons in the vicinity of aircraft. Also, sound waves have a tendency to contribute to wear and fatigue of aircraft components.
Many technical solutions have been employed in order to reduce noise generated by aircraft. These include using physical barriers attached to aircraft in order to provide a physical shield to block or attenuate sound waves and injecting gases directly into the jet engine exhaust in order to suppress noise. These solutions provide some reduction to noise levels, but normally result in some reduction in aircraft efficiency or performance. In addition, all of these solutions relate to decreasing sound waves only “downstream” from the aircraft, but do not address sound waves emanating “upstream” from the aircraft.
Therefore, it is desired to provide a relatively low-cost apparatus and method to attenuate or block aircraft noise emanating in any direction from an aircraft, without affecting aircraft performance.